If LEO was off-the-books collaborating with Backpage to allow prostitution while catching the child exploitation, that'd be a somewhat diabolical attempt at fixing a criminalization problem by turning it into a de-facto legal-and-regulated market (without legislative action to make it an actual legal-and-regulated market).

If that is, in fact, what was happening, it's kind of shame that some Congresspeople with bad strategic reasoning upset that apple cart; that'd be a superior state of affairs to one where both the prostitution and the child sex trafficking happen in the dark, beyond the reach of LEO intervention.